The invention relates to a process for the production of a flame resistant to nonflammable composite panel having a nonextrudable core mixture of a pourable, nonflammable filling material and a binder, and on both sides cover strips flexibly bonded to the core. The invention further relates to an apparatus for carrying out the process.
Composite panels are known in which metallic or nonmetallic cover strips are bonded to core layers, predominantly of inorganic nature, by bonding over the full surface with the aid of a binder. Although the core materials may be inorganic and nonflammable, owing to the lack of flexibility they are usually not capable of absorbing the deformations resulting from mechanical stresses or from thermal expansions of the cover layers. Such composite panels therefore suffer relatively often from a brittle fracture or a delamination. Furthermore, composite panels having a core layer of predominantly inorganic nature are usually moisture-sensitive or water-absorbent, as a result of which metallic cover layers may corrode, in particular if alkaline substances are used.
If inorganic core materials contain mineral constituents of great hardness or asbestos fibers, machining is only possible with special tools. Furthermore; machining is further hindered by the development of toxic dusts.
According to numerous national standards, materials having low proportions of organic substances, for example adhesive films, can be classified as nonflammable or at least flame resistant building materials or building elements.
On the other hand, core materials or organic or predominantly organic substances do not meet the requirement of flame resistance to nonflammability. If exposed to fire or other high temperatures, the decomposition of organic constituents causes large quantities of combustible gases to be set free.
It is known to reduce greatly the flammability of organic substances such as synthetic resins by the incorporation of largest possible quantities of, for example, aluminum trihydroxide. At elevated temperature, chemically bonded water becomes free and produces an effective extinguishing effect.
In DE-C3 2842858, a composite panel having two cover plates and a core of a mixture of a granular filling material and a conventional binder is described, which contains a high proportion of granular filler, in particular of aluminum trihydroxide, and a lower proportion of binder. The binder content decreases from the bounding surfaces of the cover plates to the center of the core, allowing a classification as nonflammable building elements in many countries.
A core mixture having an inorganic filler is not extrudable, which is why the production of corresponding composite panels is performed in cycles. First of all the lower cover layer, covered with an adhesive, is laid, then the core material is scattered on or otherwise applied. Finally, the upper cover layer, covered with an adhesive, is laid, and the composite panel is brought into the final form by heating, pressing and cooling.
Even with careful working, uniform, pore-free adhesive layers are not obtained, which reduces the corrosion protection. Furthermore, machine parts which serve for layer formation come into contact with adhering components, as a result of which the layer is irregularly formed.
Finally, adhesive layers of adequately high flexibility for the bonding of metallic cover layers to mineral-hard core layers cannot be applied.